STP between Fortigate HarwareSwitch and Cisco SW2960X

[DamianE]

I have a Fortigate100F (OS 7.0.13) with a Hardware Switch that have some interfaces, this hsw has the brige stp priority set to 12288 to act as root bridge.

- get sys stp
switch-priority : 12288
hello-time : 2
forward-delay : 15
max-age : 20
max-hops : 20

-get sys stp list

bridge 'Internal_LAN' prio 12288 mac 04:D5:90:FB:02:9A vd 'root'
root prio 12288 mac 04:D5:90:FB:02:9A cost 0
port 'port1' role designated state forward cost 20000 edge no rx 67 tx 129966
port 'port2' role designated state forward cost 20000 edge no rx 131637 tx 129974
port 'port3' role designated state forward cost 20000 edge no rx 131810 tx 129973
port 'port4' down

Here i can see that for the Fortigate perspective he is the root bridge 

The port1 its connected to a ABB switch that recognize the Fortigate as his root, but in port 2 and 3 has two cisco 2960x that ignore the priority of the Fortigate and one of they assume the bridge root role.

For one of Cisco (tha assumes as bridge root)

-show spanning-tree
...for exaple for one of some vlans
VLAN0050
  Spanning tree enabled protocol rstp
  Root ID    Priority    32818
             Address     2c73.a05c.8880
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32818  (priority 32768 sys-id-ext 50)
             Address     2c73.a05c.8880
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/1             Desg FWD 4         128.1    P2p Edge
Gi1/0/3             Desg FWD 19        128.3    P2p Edge
Gi1/0/23            Desg FWD 4         128.23   P2p
Gi1/0/24            Desg FWD 4         128.24   P2p
Gi1/0/25            Desg FWD 4         128.25   P2p

- show running-config
....
spanning-tree mode rapid-pvst
spanning-tree logging
spanning-tree portfast edge bpduguard default
spanning-tree extend system-id
errdisable recovery cause udld
errdisable recovery cause psecure-violation
errdisable recovery interval 120
.....
interface GigabitEthernet1/0/23
 description AR-FWC-1-P3
 switchport trunk native vlan 999
 switchport mode trunk
 spanning-tree link-type point-to-point
.....

 and for the other Cisco

- show spanning-tree
.....
VLAN0050
  Spanning tree enabled protocol rstp
  Root ID    Priority    32818
             Address     2c73.a05c.8880
             Cost        4
             Port        46 (GigabitEthernet1/0/46)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32818  (priority 32768 sys-id-ext 50)
             Address     d0ec.35bc.9e00
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/45            Altn BLK 4         128.45   P2p
Gi1/0/46            Root FWD 4         128.46   P2p
....
-show running-config
...
spanning-tree mode rapid-pvst
spanning-tree portfast edge bpduguard default
spanning-tree extend system-id
errdisable recovery cause udld
errdisable recovery cause psecure-violation
errdisable recovery interval 120
...
interface GigabitEthernet1/0/46
 description AR-FWC-OT-ESJ-1-P2
 switchport mode trunk
 spanning-tree link-type point-to-point
....

I suppose thats somthing wrong with the cisco switches configuration. It could be the stp mode that is rapid-pvst???

[abarushka]

Hello,

Is ABB switch configured to run RPVST or other standard of STP? 

[DamianE]

The abb switch run rstp...I didn't find more detail in the manuals.

[abarushka]

Hello,

Is it feasible to switch the other 2 switches to RSTP / MSTP?

FortiSwitch supports RPVSTP, however it is not clear whether FortiGate supports it.

https://docs.fortinet.com/document/fortiswitch/7.2.5/administration-guide/364618/support-for-interop... (FortiSwitch)

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Spanning-Tree-Protocol-support-for-low-end... (FortiGate)